M1 garand...11 pounds and change.
BAR...18.5 pounds.
Outfitted with all the ammunition...BAR Belt of 12 mags (240 rounds) you've got some weight. Add it to all the other gear you needed to carry...you get the picture.
Even smaller M1A1 Thompson's were very expensive to manufacture, and hence replaced with the M3 Greasegun.
Anyway...i just realized i was going to give a thorough analysis on costs, practicality, and a list of sources and a healthy dose of common sense. I changed my mind. I'll just say this...
I've fired both, and used each in a course to simulate some sort of combat conditions (i was not being shot at, and my enemy was an assortment of paper plates, targets, and milk jugs) while running, diving, and firing from all firing positions. The M1 was much easier to use, was very easy to load and fire on the go, and very accurate. The BAR (Modified M1918A2 for semi-auto) was fun, i sprayed a lot of rounds in burst and semi automatic. When it was all said and done, i fired 72 rounds from the garand and 150 from the BAR and scored more hits percentage-wise with the garand (65, a "hit" on a paper target being in a scoring ring which is a 10" radius) and something along the lines of 75 with the BAR. Conclusion...If i'm going to be running around carrying my house, the week's food supply, and all my earthly possessions while having a bunch of guys shooting at me...i'm taking the M1.
Also had to chance to fire an M1 Carbine, AR-15, Thompson, and 1903 Springfield in similar (not pseudo-reenacting) circumstances though strictly target, and my favorite out of all of them for a combat weapon would still be the M1 garand or Thompson. Both very intimidating weapons and the Thompson behaved okay at a range of 50 yards (as it was designed for that and closer ranges) while the M1 a bowling pin or enemy milk jug stands no chance within 300 yards with iron sights.